poweroff a docker buildx builder when it is idle (e.g. if it is a VM)

gistfile1.txt

#! /usr/bin/env bash

[[ "${SLEEP_TIME}" == "" ]] && SLEEP_TIME=60
[[ "${SHUTDOWN_DELAY}" == "" ]] && SHUTDOWN_DELAY=1800

wait_for_builds(){
        while (ps auxw | grep -E '[d]ocker +buildx +build') #[d] stops grep self-matching without wasting a process launch
        do
                echo "$(date --rfc-3339=seconds): builds are running" >&2
                sleep ${SLEEP_TIME}
        done
}

wait_for_shutdown_delay(){
        start_time=$(date +%s)
        until (ps auxw | grep -E '[d]ocker +buildx +build')
        do
                sleep ${SLEEP_TIME}
                if [[ "$(($(date +%s) - ${start_time}))" -gt "${SHUTDOWN_DELAY}" ]]
                then
                        poweroff
                fi
        done
}

while true
do
        wait_for_builds
        wait_for_shutdown_delay
done #no need to escape since we poweroff when done